The present invention relates to a test device and method and, more particularly, to a device and method suitable for testing a sample of foam material to detect weakness in the foam cell structure.
Foam material is used in many applications, such as those requiring thermal insulation or mechanical cushioning. Commonly, a foam material, such as a low density, lightly crosslinked, expanded polystyrene foam may be produced in the form of generally spherical beads which are on the order of 1/4 inch in diameter. The polystyrene foam defines a gas tight cell structure of low density. It is desired that such foams exhibit a high fatigue resistance. This is the result of cell wall structures which remain intact through repeated deformation of the foam material.
A number of factors affect the strength and integrity of the foam cell walls and thus affect the gas tightness of the foam and its fatigue resistance. These factors include the polymer recipe, the blowing agent recipe and loading, the crazing agents used, and the polymer and foam residence time and temperature histories. In order to be able to adjust these factors to produce the best foam properties, it is necessary to test samples of materials in which the various factors have been varied, and to quantify the fatigue resistance of each sample.
In the past, testing of foam bead samples has been accomplished utilizing laboratory equipment which compressed the samples fairly slowly to a specified percentage of their original dimensions and measured the forces required to effect this compression. Typically such equipment has been powered by a servomotor, by a pneumatic arrangement, or by a hydraulic arrangement, and had effected compression of the sample typically at the rate of approximately 1 centimeter per second. Such test devices have been found not to be as sensitive as desired in distinguishing between various samples of foam material and, further, such test devices have been found to be relatively slow to operate.
Accordingly, it is seen that there is a need for an improved device and method for testing a sample of foam material with high sensitivity and in a rapid fashion.